1. Field of the Invention
This invention relates to a method and apparatus for balancing an automotive driveline system.
2. Prior Art
In a rear wheel drive motor vehicle, the driveline comprises a transmission connected to a driveshaft which is then connected to a rear differential assembly which drives a rear drive axle. In most vehicles, the individual driveline components are balanced to provide a minimal vibration due to component imbalance. However, residual imbalances remain in the components and these imbalances may accumulate to provide an unacceptable driveline assembly.
To correct such imbalance, some vehicle manufacturers assemble the vehicle completely, then drive each assembled vehicle on a road course to establish whether the driveline imbalance of that particular vehicle is acceptable. Any perceived excessive imbalance is then corrected by diagnosing the imbalance and adding weights to the driveline at the appropriate location. Methods to balance the driveline include unbolting the driveline and reassembling the driveline with heavier fasteners to correct the imbalance, or by adding weights to the driveshaft by welding or otherwise securing a weight. These methods require excessive diagnostic time and do not capture imbalances which are marginally objectionable to some drivers, plus requires disassembly of the vehicle.
U.S. Pat. No. 5,419,192, to Maxwell et al, describes an apparatus for balancing a combined assembly of a driveshaft and axle input shaft. A system described in Maxwell is particularly for balancing a solid rear axle. The '192 device supports the differential, as shown in FIG. 4 of the '192 patent, using a first head 70 to support the front of the differential. FIG. 5 of the '192 patent shows further support for the axle, including a cradle 63 and a pair of support arms 65 and 66, as described in column 6, lines 18-69. Such mounting of the rear axle does not simulate the mounting experienced in the motor vehicle, because the cradle 63 and first head 70 do not relate to any attachment supporting the axle in the motor vehicle and therefore the fixture does not accurately simulate the driveline dynamics in the vehicle. Furthermore, the sensor 78 used in Maxwell ('192) is mounted, as shown in FIG. 6 of Maxwell, to the bracket 73 which supports the front of the differential and the center bearing. By so positioning the sensor and so supporting the driveline assembly, the true vibrations experienced by the driveline of the motor vehicle are not accurately measured, nor are the vibrations of the driveline as experienced by the body measured. The vibration of the fixture is measured.
It is therefore desirable to provide a method and fixture to mount a driveline assembly simulating the environment in a motor vehicle and directly measuring the vibrations produced in the driveline assembly which are experienced by the vehicle body.